Many electronically controlled systems use pulse width modulated (PWM) control systems. For example, modern electric motor control systems utilize pulse width modulated control signals to switch the motor drive power switching devices. Such control enhances motor efficiencies and can easily be generated by digital control systems. But, while typical motor drive control signal switching frequencies are typically in the range of 20 kHz to 30 kHz, the transmission of control signals with frequency components in this range may be undesirable from the perspective of the electromagnetic noise from inadequately shielded conductors, for example in lengthy runs of control signal cabling between the control and the motor. Many operating environments, such as automotive systems, have stringent requirements for the suppression of radiated noise in this and/or other frequency bands. Such requirements mandate that the motor control information be transmitted at lower frequencies while still conveying the appropriate duty-cycle control information to the power switching electronics. Typically, the duty-cycle information is transmitted at substantially lower frequencies, often in the hundreds of Hertz range, with the subsequent need to shift the duty-cycle encoded information up to the higher frequency signals required for the actual motor control.
While this duty cycle replication at a higher frequency can be performed by digital signal sampling and processing techniques, the overhead of relatively high clock frequencies to maintain the required translation accuracy, along with the need for high level digital content, has typically required implementation using microprocessors and associated signal processing electronics. This type of implementation also carries the need for filtered, regulated power supplies, and often in automotive applications the additional requirement of substantial transient voltage protection when located in remote locations on the vehicle. These requirements all add cost to the overall system.